GNU Octave Manual Version 3 by John W. Eaton, David Bateman, Søren Hauberg Paperback (6"x9"), 568 pages ISBN 095461206X RRP £24.95 ($39.95) |
8.8 Operator Precedence
Operator precedence determines how operators are grouped, when
different operators appear close by in one expression. For example,
‘*’ has higher precedence than ‘+’. Thus, the expression
a + b * c
means to multiply b
and c
, and then add
a
to the product (i.e., a + (b * c)
).
You can overrule the precedence of the operators by using parentheses. You can think of the precedence rules as saying where the parentheses are assumed if you do not write parentheses yourself. In fact, it is wise to use parentheses whenever you have an unusual combination of operators, because other people who read the program may not remember what the precedence is in this case. You might forget as well, and then you too could make a mistake. Explicit parentheses will help prevent any such mistake.
When operators of equal precedence are used together, the leftmost
operator groups first, except for the assignment and exponentiation
operators, which group in the opposite order. Thus, the expression
a - b + c
groups as (a - b) + c
, but the expression
a = b = c
groups as a = (b = c)
.
The precedence of prefix unary operators is important when another
operator follows the operand. For example, -x^2
means
-(x^2)
, because ‘-’ has lower precedence than ‘^’.
Here is a table of the operators in Octave, in order of increasing precedence.
statement separators
- ‘;’, ‘,’.
assignment
- ‘=’, ‘+=’, ‘-=’, ‘*=’,‘/=’. This operator groups right to left.
logical "or" and "and"
- ‘||’, ‘&&’.
element-wise "or" and "and"
- ‘|’, ‘&’.
relational
- ‘<’, ‘<=’, ‘==’, ‘>=’, ‘>’, ‘!=’, ‘~=’.
colon
- ‘:’.
add, subtract
- ‘+’, ‘-’.
multiply, divide
- ‘*’, ‘/’, ‘\’, ‘.\’, ‘.*’, ‘./’.
transpose
- ‘'’, ‘.'’
unary plus, minus, increment, decrement, and ``not''
- ‘+’, ‘-’, ‘++’, ‘--’, ‘!’, ‘~’.
exponentiation
- ‘^’, ‘**’, ‘.^’, ‘.**’.
ISBN 095461206X | GNU Octave Manual Version 3 | See the print edition |